Jacinda Ardern has announced she is stepping down as Prime Minister.

"This summer, I had hoped to find a way to prepare for not just another year, but another term - because that is what this year requires. I have not been able to do that.

"And so today, I am announcing that I will not be seeking re-election and that my term as Prime Minister will conclude no later than the 7th of February."

Ardern said she would continue as Mt Albert MP until April.

"This will give me a bit of time in the electorate before I depart, and also spare them and the country a by-election."

She said there was no special "angle" or "real reason" why she wanted to resign, only that she was "human".

"To Neve, mum is looking forward to being there when you start school next year. To Clarke, let's finally get married."

Ardern said she knew what the job of prime minister took and believed she "no longer had enough in the tank to do it justice" but there were colleagues who could.

Confident Labour can win October 14 election

She said her Government had achieved a lot and she was not standing down because she did not believe Labour could win the next election, but because she believed it could.

Ardern said the Labour caucus had agreed a vote on the leader would take place on January 22. If a leader was elected, Ardern would issue her resignation and an new prime minister would be sworn in.

A visibly and audibly emotional Ardern thanked New Zealanders for the "opportunity" to fulfil the "greatest role" of her life.

She would not, however, be drawn on who she backed to replace her in the role.

Ardern said she had hoped she would find the energy to continue as prime minister but had concluded she would be "doing a disservice" to New Zealand if she continued.

She said the caucus was surprised but understood her reasons.

“I think they could see I’d given everything and they didn’t begrudge this decision.”

She wanted to remembered as “someone who always tried to be kind”.

Asked if she would take on a role at UN as had been speculated, she said her focus had been her premiership.

“I have no plans other than spending a bit of time with my family.”

She said the UN was not her ambition.

“I’ll take each day as it comes.”

It came after she announced the election would be held on October 14.

Grant Robertson's plans

Deputy prime minister Grant Robertson issued a press release shortly after Ardern's announcement saying he would not put his name forward to be Labour's leader.

“In 2014 when I failed to secure the leadership of the Party for the second time I indicated that I would not put myself forward again. My position has not changed.”

He said he had “every confidence” there were colleagues in cacus able to fulfil the role in Ardern’s place, and who desired to “take it on”.

“They will have my full support.”

He said Ardern’s “intellect, judgement and empathy” would “mark her out as one of New Zealand’s finest leaders”.

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